Patients with genetic disease, cerebrotendinous xanthomatosis, are unusual in that their plasma cholesterol levels are normal and yet they have large tendon xanthomas. They have elevated plasma and tissue cholestanol levels and reduced chenodeoxycholic acid content of bile. The proposed studies involve the feeding of a cholesterol and cholestanol-free diet and the use of the medications, lovastatin and chenodeoxycholic acid, to reduce cholestanol levels in the blood. Cholesterol and cholestanol synthesis and the turnover of individual sterols and bile acids will be measured before and after these treatments.